Temperature dependent semiconductor module connectors

ABSTRACT

A method and structure is disclosed for forming a removable interconnect for semiconductor packages, where the connector is adapted to repeatedly change from a first shape into a second shape upon being subjected to a temperature change and to repeatedly return to the first shape when not being subjected to the temperature change. The connector can be disconnected when the connector is in its second shape and the connector cannot be disconnected when the connector is in its first shape.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention details a method and structure for forming a removableinterconnect for semiconductor packages, where the connector is adaptedto repeatedly change from a first shape into a second shape upon beingsubjected to a temperature change and to repeatedly return to the firstshape when not being subjected to the temperature change, and where theconnector can be disconnected when the connector is in its second shapeand the connector cannot be disconnected when the connector is in itsfirst shape.

2. Description of the Related Art

Due to the high cost of semiconductors, circuit boards and systems it isdesirable to provide for a method to be able to remove a semiconductormodule from an assembled circuit board without damaging the board ormodule and thereby enable field replacement capability. At present, suchcapability is problematic for organic packages, since the actuationloads required in currently available removable solutions exert forceswhich are incompatible with the organic module structures.

Existing industry solutions for removable packaging interconnectschemes, such as Land Grid Array (LGA) assemblies, apply substantialstresses to the module being connected. Today's best organic moduleinterconnect solution is the use of Ball Grid Array (BGA) solderconnections or solderable leads to make the interconnect. Solderedinterconnection schemes are not readily replaceable and factory reworkprocesses are difficult and may impact the reliability of the assembledmodule, particularly in a Pb-free soldering environment. Pin Grid Arrayinterconnects or BGA sockets do provide for more convenient modulereplacement but can be expensive and often impart changes to electricalparameters, such as increased inductance, that negatively impact deviceperformance. Moreover, these solutions may not be compatible with 1 mmgrid I/O pitch.

The best electrical and manufacturing solution available today is theuse of Land-Grid Array (LGA) structures. The LGA provides for an arrayof electrical contact pads on the bottom of the module which is broughtinto contact with a second level socket to make electrical connectionsto the circuit board. The drawback here is, in order to establishreliable connections between the module and circuit board, a substantialforce (roughly proportional to the number of module pads) must beapplied to the interposer/module assembly. Moreover, this actuationforce must be maintained for the functional life of the product. Therequired actuation force is typically excessive for organicsemiconductor packages. The high stresses imposed on the laminatesubstrate structures can cause reliability concerns associated withresin cracks, warpage, inner plane separation and PTH fractures. It isdesirable to alleviate the excessive actuation loads associated with aremovable interconnect while maintaining manufacturability, electricalperformance, reliability, field reworkability, and reasonable cost.

SUMMARY OF THE INVENTION

Disclosed is an interconnection structure (which can be an array ofconductive connectors) for use between electronic substrates (such assilicon, ceramic, or organic substrates) used for integrated circuitchips and chip carriers. With the inventive interconnection, a connectoris physically attached to a first substrate. The inventive connectordescribed herein is adapted to attach to a feature (such as atopographical feature, including a solder ball, column, opening, etc.)on a second substrate. In the present context, the first or secondsubstrate could comprise laminate printed circuit boards, chips,carriers, etc. The connector is adapted to repeatedly change from afirst shape into a second shape upon being subjected to a temperaturechange and to repeatedly return to the first shape when not beingsubjected to the temperature change. Also, the connector can bedisconnected from the feature when the connector is in its second shapeand the connector cannot be disconnected from the feature when theconnector is in its first shape.

The connector comprises a structure that repeatedly alternates betweentwo different shapes each time it is subjected to a temperature change.The connector includes a first material and a second material, where thefirst material has a different coefficient of thermal expansion than thesecond material. For example, the connector can comprise a bi-metallicstructure that utilizes two different metals having differentcoefficients of thermal expansion. The connector and the topographicalfeature can therefore form a reversible connection between the firstsubstrate and the second substrate that can be repeatedly connected anddisconnected.

The inventive connector mechanically attaches the first substrate to thesecond substrate and the connector can comprise an electrical conductorwhich also forms an electrical connection between the first substrateand second substrate. The connector is shaped to physically grasp thetopographical feature. Further, the individual connectors can beretained in an interposer like structure that is either a molded elementor non-conductive film.

In one embodiment, the connector can comprise a tubular connector thatis adapted to repeatedly change from a smaller diameter to a largerdiameter upon being subjected to a temperature change and to repeatedlyreturn to the smaller diameter when not being subjected to thetemperature change. In this embodiment, the connector can bedisconnected from the feature when the connector is the larger diameterand the connector cannot be disconnected from the feature when theconnector is the smaller diameter because the connector physicallygrasps the topographical protrusion when the connector is the smallerdiameter. The connector can include a slot that is adapted to permit theconnector to repeatedly change diameter. The connector can includeprojections adapted to surround sides of said topographical feature whenthe connector is the smaller diameter.

In a different embodiment, the second substrate includes an opening andthe connector is adapted to attach to the opening. In this embodimentthe connector changes into a smaller size upon being subjected to thetemperature change such that the connector can be disconnected from theopening when the connector is the smaller size and the connector cannotbe disconnected from the opening when the connector is the larger size.In this embodiment, the connector is shaped to provide an interferencefit with the sidewalls of the opening when the connector is the largersize. Further, the first substrate can also include an opening similarto the opening in the second substrate which allows the connector toconnect to the first substrate. The connector can be designed to allowboth ends of the connector to react similarly. Alternatively, differentends of the connector can react in opposite manners. In this situation,a first type of temperature change (e.g., an increase in temperaturefrom normal operations temperature) allows the connector to connect anddisconnect from the first substrate and an opposite type of temperaturechange (e.g., a decrease in temperature from normal operatingtemperature) allows the connector to connect and disconnect from thesecond substrate.

Thus, the invention produces interconnections that are reworkable by useof temperature, either heating or cooling, that is dependent on thematerials selected and the interconnection scheme in use. Because theinvention utilizes a mechanical connection, there is no solder to removeand minimal retention hardware (applied force) is needed since theinterconnections are self retaining. Thus, the invention provides aninterconnection that can be permanent or temporary. For example, theinvention can be used during burn in, or for permanent attachment withthe possibility of component replacement after substantial usage in thefield.

These, and other, aspects and objects of the present invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingembodiments of the present invention and numerous specific detailsthereof, is given by way of illustration and not of limitation. Manychanges and modifications may be made within the scope of the presentinvention without departing from the spirit thereof, and the inventionincludes all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription with reference to the drawings, in which:

FIG. 1 is a perspective schematic diagram of a single connection elementbetween substrates in the disengaged condition;

FIG. 2 is a perspective schematic diagram of a single connection elementbetween substrates in the engaged condition;

FIG. 3 is a top view schematic diagram of a single connector element;

FIG. 4 is a cross-sectional schematic diagram of a connection betweensubstrates;

FIG. 5 is a perspective schematic diagram of a connection betweensubstrates;

FIG. 6 is a cross-sectional schematic diagram of a connection betweensubstrates;

FIG. 7 is a cross-sectional schematic diagram of a connector;

FIG. 8 is a top view schematic diagram of a connector;

FIG. 9 is a top view schematic diagram of a connector;

FIG. 10 is a cross-sectional schematic diagram of a connector;

FIG. 11 is a cross-sectional schematic diagram of a connection betweensubstrates;

FIG. 12 is a cross-sectional schematic diagram of a connection betweensubstrates;

FIG. 13 is a cross-sectional schematic diagram of a connection betweensubstrates; and

FIG. 14 is a cross-sectional schematic diagram of connectors on aninterposer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention and the various features and advantageous detailsthereof are explained more fully with reference to the nonlimitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. It should be noted that thefeatures illustrated in the drawings are not necessarily drawn to scale.Descriptions of well-known components and processing techniques areomitted so as to not unnecessarily obscure the present invention. Theexamples used herein are intended merely to facilitate an understandingof ways in which the invention may be practiced and to further enablethose of skill in the art to practice the invention. Accordingly, theexamples should not be construed as limiting the scope of the invention.

In order to overcome the problems discussed above, the inventionpresents an interconnection for use between substrates (such as silicon,ceramic, organic, etc. substrates 18, 20 shown in FIG. 1). Thesesubstrates 18, 20 are generally used for integrated circuit chips, chipcarriers, printed circuit boards, etc. With the inventiveinterconnection shown in FIG. 1, an individual connector element 10 isattached to a first substrate 20. The connector 10 can be conductive,and has an opening 12 that is adapted to attach to a feature 16 (such asa topographical feature, including a solder ball, column, patternedfeature, opening, etc.) on a second substrate 18, as shown in FIG. 2.The connector 10 is shaped to physically grasp the topographical feature16. Thus, the inventive connector 10 mechanically attaches (throughfrictional and/or mechanical forces) the first substrate 20 to thesecond substrate 18, without the need for a chemical bond, adhesive,solder, etc. However, adhesives or solders can be used on one or more ofthe mating substrates if desired. Such connector elements would mostcommonly be implemented in large arrays to provide both signal and powerconnections for semiconductor modules.

The methodologies and materials used to form the inventive aspectsdiscussed herein include common patterning, metallurgical bonding,soldering, etc. techniques that are well-known to those ordinarilyskilled in the art. Any techniques and materials of forming suchstructures (whether now known or developed in the future) can beutilized with the invention. A detailed discussion of the same is notprovided herein so as to allow the reader to focus on the salientfeatures of the invention.

As shown in top view in FIG. 3, the connector 10 may include layers 30,32 of materials having different coefficients of thermal expansion andis therefore adapted to repeatedly change from an original first shapeinto a second shape upon being subjected to a temperature change and torepeatedly (without damage) return to the original shape when not beingsubjected to the temperature change. This temperature change can be anincrease or decrease (for example, greater than 20° C. from a normaloperating temperature and ambient temperature of the interconnection).For purposes of this application, the “normal operating temperature” isthe range of temperatures at which the device that uses the inventiveinterconnection can properly operate. For example, if a heat generatingdevice (such as an integrated circuit chip) normally operates between25° C. and 125° C. and normal ambient temperature is between −20° C. and45° C., temperatures outside the normal operating temperature andambient temperature would be below −20° C. and above 125° C. Theforegoing temperature ranges are only an example and one ordinarilyskilled in the art would understand that the inventive structure can bedesigned to be used with any temperature ranges. For example, burn-inoccurs at a higher temperature of about 140° typically. The range of thechange in size and/or shape of the connector 10 is selected such thatthe connector 10 can only be disconnected from the feature 16 when theconnector 10 is in its second shape and the connector 10 cannot bedisconnected from the feature 16 when the connector 10 is in itsoriginal shape.

The connector 10 comprises a structure that repeatedly changes shapeeach time it is subjected to a temperature change without damage.Therefore, as shown in FIG. 3, the connector 10 includes a firstmaterial 30 attached to a second material 32, where the first material30 has a different coefficient of thermal expansion than the secondmaterial 32. For example, the connector 10 can comprise a bimetallicstructure that utilizes two metals having different coefficients ofthermal expansion. Alternatively, non-metallic materials or acombination of non-metallic and metallic materials (whether now known ordeveloped in the future) can be used as the first and second materials30, 32.

The tubular connector 10 can be constructed so that it expands when itis heated or alternatively constructed so that it expands when it iscooled. For example, if the material 30 has a larger coefficient ofthermal expansion than the material 32, when the connector 10 is heatedit will expand and the connector 10 will contract when it returns tonormal operating or ambient temperature, or is cooled further. To thecontrary, if the material 30 has a smaller coefficient of thermalexpansion than the material 32, when the connector 10 is cooled belownormal operating temperature, or ambient temperature, it opens; andcloses when it warms back to ambient/normal operating temperature or isheated further.

The amount by which the connector 10 expands and contracts and thetemperature at which it does so can be selected to correspond to anyspecific design through material selection, concentration, thickness,etc. through methods well-known to those ordinarily skilled in the art.In addition, the materials of the connector 10 are selected such thatthe connector 10 will survive all temperature extremes to which itlikely will experience, so that the connector 10 can repeatedly expandand contract without damage to allow the substrates 18, 20 to berepeatedly connected and disconnected from one another. The coefficientsof thermal expansion of the materials used for the connector areselected such that the connector will remain in the original firstshape/diameter throughout the anticipated ambient temperature and normaloperating temperature, so that the connector 10 remains attached to thefeature 16 during normal operations and handling. A temperature outsidethe range of ambient temperature and normal operating temperature mustbe applied to the connector 10 in order to cause the connector 10 tochange shape/diameter to the second shape/diameter to allow the feature16 be removed from the connector 10 during replacement associated withfield service, product burn-in, field upgrade, etc. Therefore, as shownin FIG. 2, the connector 10 and the feature 16 form a separable(possibly conductive) connection between the first substrate 20 and thesecond substrate 18 that can be repeatedly connected and disconnectedwithout damaging the connector 10, the feature 16, or either substrate18, 20.

Further, as shown in cross-sectional view in FIG. 4, and the connector10 can comprise an electrical conductor which also forms an electricalconnection between wiring 40 in the first substrate 20 and secondsubstrate 18. If the connector 10 is conductive, the wiring 40 can be indirect contact with the connector. Similarly, if the feature 16 isconductive, it can be connected to the wiring in the first substrate 20as shown in FIG. 4. However, the feature 16 does not need to contact thefirst substrate 20 as shown in FIG. 6. Alternately, the wiring can becontinuous under the connector 10 and the feature 16 as shown by thedashed line in FIG. 4.

In the embodiment shown in FIGS. 1–4, the connector 10 can comprise atubular connector 10 that is adapted to repeatedly change from a smallerdiameter to a larger diameter upon being subjected to a temperaturechange and to repeatedly return to the smaller diameter when not beingsubjected to the temperature change. In the embodiment shown in FIGS.1–4, the connector 10 can be disconnected from the feature 16 when theconnector 10 is the larger diameter and the connector 10 cannot bedisconnected from the feature 16 when the connector 10 is the smallerdiameter because the connector 10 physically grasps the topographicalprotrusion 16 when the connector 10 is the smaller diameter. Theconnector 10 can include a slot 14 that is adapted to permit theconnector 10 to repeatedly change diameter without damage.

Therefore, the embodiment shown in FIGS. 1–4 includes a mini sleeve-likestructure which slips over one module ball or column and can ‘grab’ ontothe module ball or column. The grabber (connector 10) can be, forexample, a bimetallic structure which consistently changes shape withtemperature (a product of the bi-metallic structure itself). In thisexample, the grabber 10 opens up during an elevated temperature(significantly above operational temperatures for the assembly, butbelow any critical temperature for the module, ball or column), allowingthe ball or column 16 to be inserted, and when the temperature islowered, the bi-metallic returns to its original state, closing and‘grabbing’ the ball or column 16.

In addition, as shown in FIGS. 5 and 6, the connector 10 can includeeagle claw-like or flower-like projections 50 adapted to surround sidesof the feature 16 when the connector 10 is the smaller diameter. Theprojections 50 can comprise features attached to the tubular connectoror can comprise an integral patterned part of the connector 10. FIG. 5illustrates a perspective view before the connector 10 is attached tothe feature 16. FIG. 6 illustrates a cross sectional view illustratingthe projections 50 wrapping around the feature 16, thereby mechanicallygrasping the feature 16. When compared to the embodiment shown in FIGS.1–4, the embodiment shown in FIGS. 5 and 6 provides additionalinterconnection strength by not only grasping the sides of the feature16 using the tubular portion 10, but also by wrapping around the roundedfeature 16. In the embodiment shown in FIGS. 1–6, the connector 10 ispermanently attached (bonded, soldered, etc.) to the first substrate 20and is selectively connected to the feature 16 on the second substrate18. However, in the following embodiment, the connector (which islabeled 70 in the following embodiment) can be temporarily connected toboth substrates 18, 20.

More specifically, in the embodiment shown in FIGS. 7–12, the secondsubstrate 18 includes an opening 114 and the connector 70 is adapted toexpand within the opening 114 so as to attach to the opening 114 (seeFIG. 12). In this embodiment the connector 70 changes into a smallersize upon being subjected to the temperature change such that theconnector 70 can be disconnected from the opening 114 when the connector70 is the smaller size and the connector 70 cannot be disconnected fromthe opening 114 when the connector 70 is the larger size. In thisembodiment, the connector 70 is shaped to provide an interference fitwith the sidewalls of the opening 114 when the connector 70 is thelarger size. Fabricating the opening 114 with conductive sidewalls willfurther provide for electrical contact across the connection formed whenconnector 70 is fully engaged.

FIG. 7 illustrates a cross sectional view of the connector 70 when it isthe smaller size and FIG. 10 illustrates a cross sectional view of theconnector 70 when it is the larger size. Thus, when the connector 70 isheated or cooled outside ambient temperature and normal operatingtemperature, it takes the shape illustrated in FIG. 7. At ambienttemperature and normal operating temperature, the connector takes theshape shown in FIG. 10. The connector 70 can comprise a beam orrectangular shape, as shown in top view in FIG. 8. Alternatively, theconnector 70 can comprise a cylinder shape, as shown in top view in FIG.9. The cross-sectional views shown in FIGS. 7 and 10 are drawn alonglines X–X′ in FIGS. 8 and 9. In addition, the claw-like or flower-likeprojections 50 shown in the previous embodiment can be designed toexpand when at ambient temperature and normal operating temperature, sothat the connector 10 can be inserted into an opening and maintainedwithin the opening while the projections expand outward.

Thus, this embodiment illustrates a “split pin” structure. As the pin iskept at ambient and normal operating temperature, the opposite ends tomove in opposite directions, expanding the shape and size of the pin. Asthe pin is heated or cooled outside ambient and normal operatingtemperature, the end(s) narrow/close, allowing the pin to be insertedinto a via or opening. After the pin is inserted into the via/hole inthe module, it is allowed to return to ambient and/or normal operatingtemperature, causing the end of the pin to open, grabbing the inside ofthe via and providing a connection.

The connector itself again includes one material 74 having a firstcoefficient of thermal expansion lined with an exterior second material72 having a different coefficient of thermal expansion. In addition aslot, trench, slit, etc. 76 is molded, patterned, machined, etc. intothe connector 70 to allow the sides of the connector to separate asshown in FIG. 10. Further, the connector 70 can be divided into a tophalf and bottom half, as shown by the dotted line in FIG. 7, with thetop half reacting differently to a temperature change than the bottomhalf. For example, the top half could contract when heated, while thebottom half could contract when cooled. In this situation, a first typeof temperature change (e.g., an increase in temperature) allows theconnector 70 to connect and disconnect from the first substrate 20 and asecond, opposite type of temperature change (e.g., a decrease intemperature) allows the connector 70 to connect and disconnect from thesecond substrate 18. This would allow the connector 70 to be selectivelyconnected/disconnected to one substrate 18 will being cooled, andselectively connected/disconnected to the second substrate 20 will beingheated. This feature of the invention allows the connector to beconnected to the substrates at different manufacturing processing steps,thereby providing more flexibility in manufacturing, testing, andservicing.

The opening 114 can take on any appropriate shape. For example, theopening 114 can be rectangular, or as shown in FIGS. 11 and 12 can matchthe shape of the expanded connector 70. In this example, since the endof the connector 70 takes on a trapezoidal shape in cross-section, theopening 114 can also be formed as a trapezoidal shape to match theexpanded shape of the connector 70. In addition, in this embodiment,both substrates 18, 20 can include openings 114. Alternatively, theconnector 70 could be permanently attached to one of the substrates andselectively connected to the other substrate, as with the previousembodiments. In addition, as shown in FIG. 12, in all the embodimentsherein, the wiring 40 can line the openings 114 to provide additionalcontact area for a conductive connector 70.

Any of the foregoing structures can be combined such that one structureis used to attached to one substrate and a different type of structureis used to attach to the other substrate. For example, as shown in FIG.13, the top half of the connector could be similar to the split pinstructure shown in FIGS. 7–12, and the bottom half of the connectorcould be similar to the tubular connector and illustrated in FIGS. 1–6.This structure (and any of the foregoing structures) can be formed usingan interposer 144 as shown in FIGS. 13 and 14. With the invention,either entire connectors, or half-connector structures can betemporarily or permanently connected to the interposer 114.

In an example shown in FIG. 14, the top half of one type of connector140 is connected to one side of the interposer 144 and the bottom halfof a different type of connector 142 is connected to the other side ofthe interposer 144. The interposer 144 could be an insulator which wouldprevent the interposer 144 from causing unintended short circuits if theinterposer 144 were to remain in the final structure or it could be aconnector if it is utilized between two conductive connectors to allowthe connectors to remain in electrical contact.

The interposer 144 is useful in arranging multiple connectors into anarray format. Thus, the interposer can be utilized as a surface on whichthe connectors can be manufactured. Then, an interposer holding an arrayof manufactured connectors can be positioned to allow the connectors tobe permanently or temporarily connected to one substrate. Then, theinterposer can be removed (or the interposer can remain on thestructure). Next, after the array of connectors have been connected toone substrate, a second substrate can be brought into position such thatthe connectors can be permanently or temporarily connected to the secondsubstrate. Thus, as shown above, the interposer 144 can be used only asa temporary holding device to manufacture and position the connectors,or the interposer 144 can remain as a permanent part of the finalstructure. Further, as discussed above, the interposer can comprise aconductor or an insulator.

Thus, the invention produces interconnections that are reworkable by useof temperature, either heating or cooling, that is dependent on thematerials selected and the interconnection scheme in use. Because theinvention utilizes a mechanical connection, there is no solder to removeand minimal retention hardware (applied force) is needed since theinterconnections are self retaining. Thus, the invention provides aninterconnection that can be permanent or temporary. For example, theinvention can be used during burn-in or for permanent attachment withthe possibility of component replacement after substantial usage in thefield.

With proper selection of bimetallic materials and combinations thereof,one can design a system that can be easily assembled and/or reworked atelevated or cryogenic temperatures, be self-retaining and potentiallyfield replaceable, yet not exert undue retention force on the module.The invention is also advantageous because it permits theinterconnection to be disconnected by being cooled, which substantiallyreduces of the possibility of overheating either structure (which couldmelt or destroy thermally sensitive (soldered) connections). Otherapplications of the invention include both die and module burn-in. Theinvention is useful with practically all known interconnection schemes.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

1. An interconnection between substrates, said interconnectioncomprising: a connector attached to a first substrate; and a feature ona second substrate, wherein said connector is adapted to attach to saidfeature, wherein said connector is adapted to repeatedly change from afirst shape into a second shape upon being subjected to a temperaturechange and to repeatedly return to said first shape when not beingsubjected to said temperature change, and wherein said connector can bedisconnected from said feature when said connector is in said secondshape and said connector cannot be disconnected from said feature whensaid connector is in said first shape.
 2. The interconnection accordingto claim 1, wherein said connector comprises a first material and asecond material, wherein said first material has a different coefficientof thermal expansion than said second material.
 3. The interconnectionaccording to claim 1, wherein said connector attaches said firstsubstrate to said second substrate.
 4. The interconnection according toclaim 1, wherein said connector comprises an electrical conductor. 5.The interconnection according to claim 1, wherein said feature comprisesa topographical feature and said connector is shaped to physically graspsaid topographical feature.
 6. The interconnection according to claim 1,wherein said connector and said feature form a temporary connectionbetween said first substrate and said second substrate.
 7. Theinterconnection according to claim 1, wherein said connector and saidfeature are adapted to connect to one another mechanically.
 8. Aninterconnection between substrates, said interconnection comprising: atubular connector attached to a first substrate; and a feature on asecond substrate, wherein said connector is adapted to attach to saidfeature, wherein said connector is adapted to repeatedly change from asmaller diameter to a larger diameter upon being subjected to atemperature change and to repeatedly return to said smaller diameterwhen not being subjected to said temperature change, and wherein saidconnector can be disconnected from said feature when said connector issaid larger diameter and said connector cannot be disconnected from saidfeature when said connector is said smaller diameter.
 9. Theinterconnection according to claim 8, wherein said connector comprises afirst material and a second material, wherein said first material has adifferent coefficient of thermal expansion than said second material.10. The interconnection according to claim 8, wherein said connectorincludes a slot adapted to permit said connector to repeatedly changediameter.
 11. The interconnection according to claim 8, wherein saidconnector comprises an electrical conductor.
 12. The interconnectionaccording to claim 8, wherein said feature comprises a topographicalprotrusion and said connector is shaped to physically grasp saidtopographical protrusion when said connector is said smaller diameter.13. The interconnection according to claim 8, wherein said connectorfurther comprises projections adapted to surround sides of said featurewhen said connector is said smaller diameter.
 14. The interconnectionaccording to claim 8, wherein said connector and said feature areadapted to connect to one another mechanically.